1. Field of the Invention
The present invention relates to a power supply apparatus and an image forming apparatus including the same.
2. Description of the Related Art
In recent years, because the size of image data and program files has increased, image forming apparatuses have come equipped with a hard disk drive (hereinafter referred to as HDD) capable of storing that information. HDDs have a high likelihood of malfunction compared with semiconductor memory and other memory apparatuses. For instance, if a user switches off the main power supply to an image forming apparatus while the head of the HDD is accessing data, the head cannot withdraw to a safety zone and HDD failure or loss of data can occur. Consequently, some sort of method is needed to protect the HDD when the main power supply is turned off. At the same time, image forming apparatuses have various loads (e.g. motor, heater, high-voltage power supply, and the like). When a user notices an abnormality in a load and switches off the main power supply, the power supply to these loads must be cut off immediately.
Japanese Patent Laid-Open No. 2011-22775 describes an invention in which a relay is connected in parallel to a main power switch that switches the supply of electrical power from an alternating-current source on and off, and even if the main power switch is turned off, the electrical power from the alternating-current source continues to be supplied for a period of time via the relay. Moreover, Japanese Patent Laid-Open No. 2011-22775 discloses that the electrical power supply to loads such as the motor can be cut off instantaneously with a relay provided so as to operate in conjunction with a status signal that indicates whether the main power switch is on or off.
According to Japanese Patent Laid-Open No. 2011-22775, although the supply of electrical power to loads such as the motor is cut off immediately when the main power switch is turned off, there is an advantage in that electric power can continue to be supplied to the HDD. However, a new problem arises in the invention described in Japanese Patent Laid-Open No. 2011-22775 in that a large number of switches and relays are needed.